Directed growth cone movement, mainly an actin-based cell motility, guides the pathfinding of a growing neurite during the formation of nervous system. Specific actin-associated proteins and actin-based motors have been shown to function in specific aspects of growth cone motility, suggesting that sets of proteins act together to generate and control actin-based motility in axonal pathfinding. The hypothesis to be tested in this proposal is that specific myosins play distinct roles in neuronal filopodial and lamellipodial motility and growth cone turning. To test the hypothesis, chromophore-assisted laser inactivation (CALI) technique in combination with various pharmacological inhibitors will be employed to dissect the function of myosins in vivo. The following specific aims will be addressed: Aim 1. To determine the specific roles of a specific myosin in neuronal filopodial and lamellipodial motility. Many studies have indicated that different myosins exhibit specific cellular localization and play unique roles in growth cone motility. However, the specific roles of many myosins in specific motility events remain to be resolved. Here, we will examine (a) the role of MYO1B, non-muscle myosin IIA, myosin Va, and myosin VI in neuronal filopodial F-actin retrograde flow and (b) the involvement of MYO1B, myosin IIA and IIB, myosin Va, and myosin VI in filopodia and lamellipodial dynamics. Aim 2. To determine the roles of myosins in growth cone turning. It has been shown that inactivation of MYO1C induces lamellipodial expansion and repetitive asymmetric inactivation leads to growth cones turning. Here, we will examine the roles of MYO1B, myosin IIA, myosin Va, and myosin VI in growth cone turning. These studies will establish which myosin play roles in growth cone turning as a myosin may function in filopodial and/or lamellipodial movement, but may not in determining the direction of growth cone turning [unreadable] [unreadable]